Hybrid materials containing organic polymers and metal–organic frameworks (MOFs) have attracted attention for their potential to harness both diverse functionality and high processability, but their fabrication is challenged by incompatibilities of the parent components. The poor solubility of MOFs hinders uniform dispersion throughout a polymer matrix and may cause aggregation that is not only detrimental to the permeability of substrates, but also limits the structural integrity of the polymer. Meanwhile, polymer chains can block or penetrate the porous structures and compromise MOF functionality by reducing surface area and pore size. We report a versatile method of covalent hybridization through post-synthetic ligand exchange to form a cross-linked polymer–MOF composite. The resulting network structure allows for the formation of robust, monolithic composites with variable MOF loadings that may exceed 80% wherein ligand exchange is limited to surface sites so as to fully preserve MOF surface area and porosity. The synthesis can be performed from a diverse set of inexpensive starting materials, encouraging the design of new functional materials across a wide range of applications.

This Perspective is part of the Up-and-Coming series.

Morphological behavior of PS−PLA bottlebrush copolymers with a compositional gradient along the backbone was investigated by small-angle X-ray scattering (SAXS) analysis and compared to that of their block copolymer analogs. Side chain-symmetric gradient copolymers with varying volume fractions were prepared by one-step ring-opening metathesis polymerization of the corresponding exo-and endo-norbornenefunctionalized macromonomers of similar lengths. The morphological map constructed using the SAXS data revealed a wide cylindrical morphology window, including for symmetric compositions, well-ordered lamella morphologies at very low PS volume fractions, and the formation of a rare bicontinuous gyroid morphology. In addition to the highly asymmetric nature of the morphology diagram, the domain spacings obtained for gradient bottlebrush copolymers were significantly smaller (by 30−40%) than the corresponding bottlebrush block copolymer analogs, which was attributed to a nonperpendicular orientation of the gradient bottlebrush backbone at the domain interface. Side chain-asymmetric gradient bottlebrush copolymers were synthesized from PS and PLA macromonomers of different lengths and were demonstrated to assemble into well-ordered cylindrical and lamella morphologies. The results of these studies demonstrate that the gradient interface plays an important role in determining molecular packing during bottlebrush copolymer self-assembly. A rich morphological behavior of the gradient bottlebrush copolymers combined with their "user-friendly" onestep synthesis provides a robust and versatile platform for nanostructured material-design and fabrication.

Discrete metal-organic polyhedra (MOPs) containing copper(ii), palladium(ii), and iron(ii) nodes were synthesized as fillers for mixed-matrix materials (MMMs) with a polyvinylidine fluoride (PVDF) polymer phase and contrasted against an MMM containing a metal-organic framework, MOF-5. When a given MOP was soluble in the precursor solutions, the resulting MMMs were thin, flexible, and homogeneous based on microscopy and SEM imaging. Analogous MMM formation using either insoluble MOPs or the inherent insoluble MOF-5 showed a higher degree of phase separation and inhomogeneity. Even when a MOP was not fully soluble, a significant particle size decrease was observed in contrast to the MOF-5 materials wherein the crystallites remained largely intact. This is a consequence of solubilizing the MOP fillers into the polymer solvent. The crystallinity and thermal stabilities of the MMMs were compared to pure PVDF using powder X-ray diffraction, and differential scanning calorimetry, indicating that the incorporation of MOPs both decreased overall crystallinity as well as increased thermal stability. In addition, MMMs containing PdMOP and FeMOP showed improved gas permeabilities relative to pure PVDF for H2, N2, CH4, and CO2, with the 10 wt% FeMOP membrane more selective for CO2 over N2 and H2.